.\" $Id$
.TH BW_PIPE 8 "$Date$" "(c)1994 Larry McVoy" "LMBENCH"
.SH NAME
bw_pipe \- time data movement through pipes
.SH SYNOPSIS
.B bw_pipe
[
.I "-m <message size>"
]
[
.I "-M <total bytes>"
]
[
.I "-P <parallelism>"
]
[
.I "-W <warmups>"
]
[
.I "-N <repetitions>"
]
.SH DESCRIPTION
.B bw_pipe
creates a Unix pipe between two processes and moves 
.I "total bytes"
through the pipe in 
.I "message size"
chunks (note that pipes are typically sized smaller than that).  
The default
.I "total bytes"
is 10MB and the default
.I "message size"
is 64KB.
.SH OUTPUT
Output format is \f(CB"Pipe bandwidth: %0.2f MB/sec\\n", megabytes_per_second\fP, i.e.,
.sp
.ft CB
Pipe bandwidth: 4.87 MB/sec
.ft
.SH MEMORY UTILIZATION
This benchmark can move up to six times the requested memory per process.
There are two processes, the sender and the receiver.
Most Unix
systems implement the read/write system calls as a bcopy from/to kernel space
to/from user space.  Bcopy will use 2-3 times as much memory bandwidth:
there is one read from the source and a write to the destionation.  The
write usually results in a cache line read and then a write back of
the cache line at some later point.  Memory utilization might be reduced
by 1/3 if the processor architecture implemented "load cache line"
and "store cache line" instructions (as well as getcachelinesize).
.SH ACKNOWLEDGEMENT
Funding for the development of
this tool was provided by Sun Microsystems Computer Corporation.
.SH "SEE ALSO"
lmbench(8).
.SH "AUTHOR"
Carl Staelin and Larry McVoy
.PP
Comments, suggestions, and bug reports are always welcome.
